The present invention relates to the field of memory devices. More particularly, the present invention relates to a method for filling vias in memory devices with metal.
A well known semiconductor memory component is a random access memory (RAM). RAM permits repeated read and write operations on memory elements. Typically, RAM devices are volatile, in that stored data is lost once the power source is disconnected or removed. Non-limiting examples of RAM devices include dynamic random access memory (DRAM), synchronized dynamic random access memory (SDRAM) and static random access memory (SRAM). DRAMs and SDRAMs typically store data in capacitors which require periodic refreshing to maintain the stored data. The periodic refreshing process drains power, thus lowering the amount of time computing devices such as lap top computers can be used apart from a constant power source.
Recently resistance variable memory elements, which include programmable conductor random access memory (PCRAM) elements, have been investigated for suitability as semi-volatile and non-volatile random access memory elements. Generally a PCRAM element includes an insulating dielectric material formed of a chalcogenide glass disposed between two electrodes. A conductive material, such as silver, is incorporated into the dielectric material. The resistance of the dielectric material can be changed between high resistance and low resistance states. The programmable conductor memory is typically in a high resistance state when at rest. A write operation to a low resistance state is performed by applying a voltage potential across the two electrodes.
When set in a low resistance state, the state of the memory element will remain intact for minutes or longer after the voltage potentials are removed. Such material can be returned to its high resistance state by applying a reverse voltage potential between the electrodes from that used to write the element to the low resistance state. Again, the highly resistive state is maintained once the voltage potential is removed. This way, such a device can function, for example, as a resistance variable memory element having two resistance states, which can define two logic states.
With specific reference to FIGS. 1A-1C, one method of forming a conventional PCRAM cell is shown. A first conductor 12 is formed on a substrate 10. Then, an insulator 14 is formed on the first conductor 12, and a via 18 is formed in the insulator 14. Then, a metallic material 16 such as silver is deposited on the insulator 14 and in the via 18, after which a polishing step removes the metallic material 16 from the surface of the insulator 14. Then, a chalcogenide glass 22 is deposited over the metallic material 16, followed by a metal-containing layer 24 and a second conductor 26. Then, a second polishing step removes the chalcogenide glass 22, metal-containing layer 24 and second conductor 26 everywhere but within the via 18.
One undesirable aspect which has been observed with the above-described method is that the first polishing step sometimes pulls the metallic material 16 out of the via 18 leaving no metal in the via 18 as shown in FIG. 1B. In addition, an undesired build up of slurry residual in the via 18 from the first polishing step has also been observed.